Integrated circuit technology continues to advance at a rapid pace, with many circuit technologies being implemented using semiconductor fabrication processes. With the advancement of semiconductor circuit fabrication, consideration is given to various aspects, including maximizing efficiency, lowering manufacturing cost, and increasing performance. With these goals in mind, low dielectric constant (low k) and ultra-low dielectric constant materials are now being considered as favorable for various insulting layers, sometimes referred to as interlevel and intermetal dielectrics, used in a semiconductor circuit. In the past, such insulating layers were implemented using silicon dioxide (i.e., SiO.sub.2). Silicon dioxide has a dielectric constant, sometimes referred to in the art by the value k, on the order of 4.0. However, silicon dioxide is now being replaced with progressively lower dielectric constant materials. Carbon-doped oxide (CDO), produced using methylsilsesquioxane (MSQ) precursors with spin-on processes, as well as chemical vapor deposition (CVD) processes using various carbon-containing precursors, is a class of materials having a significantly lower dielectric constant (e.g. commonly 2.2–2.9). In CDO dielectric materials, the regular SiO2 matrix has bonding such as Si—CH3 in the place of some of the Si—O bonds, which lowers the dielectric constant of the material. CDO materials can be made by spin-on or chemical vapor deposition techniques and are sold under various trade names, such as CORAL®, a CVD organo-silicon glass (OSG) commercially available from Novellus Systems, Inc., and Black Diamond™, another CVD material commercially available from Applied Materials, Inc. JSR Corporation also has a CDO which is an MSQ-based spin-on dielectric film known as LKD-5109, with a dielectric constant of 2.2. By reducing the dielectric constant, such as is achieved by these CDO materials, semiconductor devices may be constructed using thinner films for insulating layers. This approach decreases device size and cost. Performance is also increased, such as by way of example where metal lines (e.g., copper) are formed closer together due to the thinness of the low-k or ultra-low-dielectric constant material which separates the metal from other layers/regions/devices.
While CDO materials have advance various goals in the formation of semiconductor circuits, the present inventors have observed a considerable drawback in the use of such low and ultra-low dielectric constant (known as low-k or ultra-low-k) materials. Specifically, during the formation of semiconductor circuits, and as also detailed later, it is known in the art to use photoresist materials as a mask for etching through an insulating layer, such as a silicon dioxide layer, to provide for example, vias, trenches, or other areas through which electrical contact may be made to various points covered by the insulating layer. Once the photoresist has served its masking purpose, it along with any related residue, is removed. This process is sometimes referred to as a clean-up or a strip, and such removal has been achieved in the art by various different processes. However, the present inventors have observed that these traditional photoresist-removal processes, while effective for ordinary silicon dioxide, negatively affect a lower dielectric constant material such as a CDO type of dielectric material. For example, one prior art photoresist-removal process uses an oxygen-based plasma at high temperature, that is, on the order of 250.degree. C. However, when used with a CDO type of dielectric material, the prior art use of an oxygen-based plasma causes the oxygen in the plasma to react with the CDO dielectric material; in other words, rather than being inert with the CDO as is desired, the oxygen may cause the CDO to convert in part to SiO2 and/or to diminish in width and/or in depth. Further complicating this issue is that manufacturers provide CDO-type materials that contain different percentages of, for example, carbon. As a result, the present inventors have observed a corresponding difference in the rate of carbon loss and width and/or depth loss of the CDO type of film when the film is exposed to oxygen-containing plasma. For example, in the past, rates of degradation or loss and width and/or materials were observed on the order of 25 Angstroms per minute exposure to oxygen-containing plasmas while more recently rates of degradation on the order of 100 Angstroms per minute have been observed. Thus, there is a need to reduce this degradation, and indeed such a need will continue should low k materials continue to show degradation on reaction with standard (e.g., O.sub.2,250.degree.C.) photoresist removal processes.
In view of the above, there arises a need to address the drawbacks of the prior art and to provide a method for effectively removing photoresist from low-k and ultra-low dielectric constant materials, as is achieved by the preferred embodiments described below.